Conventionally, various methods of detecting knocking (knock) that may occur in an internal combustion engine have been proposed. For example, there is a technique of determining occurrence of knocking when magnitude of vibration in an internal combustion engine is greater than a threshold. However, even when the knocking has not occurred, vibrations due to, e.g., closing of intake valves and exhaust valves may exceed the threshold. In this case, it may be erroneously determined that the knocking occurred, although the knocking did not occurred. Accordingly, such a technique has been proposed that the presence or absence of the knocking is determined based on a waveform of vibration for giving consideration to characteristics such as a crank angle at which the vibration occurs and/or attenuation factor, i.e., characteristics other than the magnitude.
Japanese Patent Laying-Open No. 2004-353531 has disclosed a knock control device of an internal combustion engine that precisely determines whether knock occurred or not, using a waveform, and thereby appropriately control a drive or operation state of an internal combustion engine. The knock control device disclosed in Japanese Patent Laying-Open No. 2004-353531 includes a signal detector detecting a vibration waveform signal generating in the internal combustion engine, a frequency separator separating the vibration waveform signal detected by the signal detector into a plurality of frequency components, a waveform setting unit determining a shape of a knock waveform according to values each obtained by magnitude integration that is performed on each of the plurality of frequency components separated by the frequency separator for each predetermined section of a predetermined crank angle, a knock determining unit determining whether the internal combustion engine knocked or not, based on the knock waveform shape set by the waveform shape setting unit, a knock controller controlling an operation state of the internal combustion engine according to a result of the determination by the knock determining unit, and an ideal waveform setting unit that presets, as an ideal knock waveform, an ideal knock waveform shape of a vibration waveform signal occurring in the internal combustion engine. The waveform setting unit corrects the waveform to decrease knock magnitude when an magnitude rising portion preceding a peak of the knock waveform has an magnitude rising rate smaller than that of the ideal knock waveform.
According to the knock control device disclosed in this publication, a vibration waveform signal that occurs in the internal combustion engine and is detected by the signal detecting unit is separated into a plurality of frequency components by the frequency separator. The waveform setting unit sets the knock waveform according to the value obtained by magnitude integration that is performed on the frequency components thus separated for each predetermined section of a predetermined crank angle. Based on the knock waveform, the knock determining unit determines whether the internal combustion engine knocked or not. Based on a result of this determination, the knock controller controls the operation state of the internal combustion engine. In this manner, the vibration waveform signal generated in the internal combustion engine is separated into the plurality of frequency components, and the knock waveform is set by the value obtained by the magnitude integration that is performed on the plurality of separated frequency components for each predetermined section of the predetermined crank angle so that the knock waveform can be represented as the sum or total of the respective vibration modes. According to this knock waveform, it is possible to determine precisely whether the internal combustion engine knocked or not, so that the operation state of the internal combustion engine is appropriately controlled. When the magnitude rising portion preceding the peak of the knock waveform rises at a lower magnitude rising rate than the ideal knock waveform, this portion may be confused with the knock waveform, and therefore is corrected to decrease the magnitude. Since large variations are present in magnitude rising rate of the magnitude rising portion preceding the peak of the knock waveform, correction is performed when the magnitude rising rate is higher than that of the ideal knock waveform, and the correction is performed to decrease the magnitude when the magnitude rising rate is lower than that of the ideal knock waveform. Thereby, it is possible to prevent erroneous detection of knock from a noise waveform different in shape from that of the knock.
When the comparison between the detected waveform and the ideal knock waveform is performed with reference to the peak of the waveform, as is done in the knock control device disclosed in Japanese Patent Laying-Open No. 2004-353531, the crank angle of the peak must be precisely detected. When the crank angle of the peak is erroneously detected, the comparison between the detected waveform and the ideal knock waveform cannot be performed correctly, and an error may occur in determination of whether the knocking occurred or not. However, Japanese Patent Laying-Open No. 2004-353531 has neither disclosed nor suggested a manner of precisely detecting the crank angle, e.g., of the peak that provides a reference for the comparison between the detected waveform and the ideal knock waveform. Therefore, this device is susceptible to further improvement for correctly comparing the detected waveform with the ideal knock waveform and precisely determining whether the knocking occurred or not.